Crystallization and X-ray diffraction analysis of an antifungal laticifer protein

An osmotin (CpOsm) from the latex of Calotropis procera has been crystallized in both tetragonal and trigonal forms suitable for structure determination. Crystallographic studies of CpOsm are of great interest because limited information is available concerning the structure of latex proteins and CpOsm has previously been shown to interact with the spore membranes of some plant pathogenic fungi, thus impairing spore germination and hyphal growth. CpOsm crystals were grown using 0.1 M HEPES buffer pH 7.5, 26% PEG 4000, 0.2 M ammonium sulfate (space group P4₃) or using 0.1 M HEPES buffer pH 7.5, 35% MPD, 0.7 M ammonium sulfate (space group P3₁12). X-ray diffraction data were collected to 2.17 Å (P4₃) and 1.80 Å (P3₁12) resolution and molecular-replacement analyses produced initial phases for both crystal forms.